I know it's been done before, but here it is again with a well-known example image (credit to NASA (http://visibleearth.nasa.gov/view.php?id=73934)). Although it would be nicer if the resolution were higher (and the oceans not strangely pixelated because of it). These basic steps are one way to bring relief and a bit of color to a flat, greyscale height map. Yes, it's upside down. Start at the bottom.

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Image 6: Final result.

Image 5: Apply colors to different altitudes.
Duplicate the original layer, drag to top of layers panel, set style to color, apply gradient map.
(Image > Adjustments > Gradient Map > Double click the colorful box to edit the gradient)
Click the bottom arrows along the color bar to change the colors in the area below.
Drag the bottom arrows along the color bar to adjust the altitude range affected by each color.
Fiddle to your heartís content.

Image 4: The image as it looks right now.

Image 3: Make it look bumpy. You can duplicate the levels-adjusted layer (like I did) or work with it directly.
(Filters > Render > Lighting Effects)
Youíll want Directional light type. (drag the black dot in the preview box to change the light direction)
Change the Texture Channel to the channel that you created.
And despite all evidence to the contrary, White is NOT high. Not this time.
Other than those, play with it and see what happens.
When you find something you like, Save... it for later.